Many insurance companies offer usage-based vehicle insurance where insurance ratings and premiums are determined based on a driver's vehicle usage. An important usage factor is vehicle speed or how fast the driver is driving. Various means can be used to determine the speed of a vehicle. For example, monitoring devices that interface with the on-board diagnostic port of the vehicle can be used to monitor the vehicle speed. Other systems rely on Global Positioning System (GPS) technology that is either built into the vehicle or from the use of GPS sensors on a mobile device (e.g., a smartphone). Still other systems make use of accelerometer sensors in mobile devices to estimate the speed of the vehicle. However, monitoring devices can be expensive or require expert installation, while GPS may not be available all the time or even accurate in some situations (e.g., during low speeds). Further, mobile device-based GPS can be a significant drain on the batteries of the mobile device. On the other hand, accelerometer-based methods can be more cost effective than on-board monitoring devices and use less energy than some GPS solutions.